Blood urea is the end product of protein breakdown and is excreted from the body by the kidneys. Elevated levels of urea can be found in persons on a high protein diet or after a long period of fasting. High levels of urea can also be found in renal diseases.
Creatinine is a by-product of muscle function and is related to the muscle mass of a person. It is excreted by the kidneys. Elevated levels of creatinine are seen in renal diseases as the creatinine is accumulated in the blood and not excreted by the diseased kidney. Elderly people or a person who is on high meat diet may have elevated creatinine levels.
Decrease in serum creatinine is seen in pregnancy and in conditions associated with muscle wasting.